For years single use and rechargeable nickel-cadmium (NiCd) batteries have been employed to power portable radios, shavers, laptop computers, non-volatile memory components, etc. NiCd batteries exhibit good capacity (i.e., the length of useable time between charges), reusability (i.e., the ability to be recharged) and service life (i.e., the length of time a battery may be used before a minimum useful battery capacity, such as 60% of the battery's maximum or "initial" capacity, is unachievable by re-charging). However, due to environmental concerns over the disposal of heavy metals such as cadmium, alternative battery technologies have been developed.
Nickel metal hydride (NiMH) batteries offer a more environmentally friendly alternative to NiCd batteries. NiMH batteries have better capacity than NiCd batteries, but suffer from poor battery service life in hot operating environments (e.g., above 36.degree. C.). For example, for operating environments having a temperature of about 28.degree. C. or less, the service life of a NiMH battery is about 36 months. However, for operating environments having a temperature of about 36.degree. C. or higher, the service life of a NiMH battery is only about 19.5 months.
Because batteries typically are rated based on the worst case operating environment (e.g., about 40.degree. C. for NiMH batteries) even though actual battery operating environments rarely approach the worst case operating environment, NiMH batteries often are changed prematurely. The high costs associated with service calls, service disruption and battery disposal that accompany battery replacement necessitate longer battery service life.